In MIMO (multiple input multiple output) OFDM (orthogonal frequency division multiplexing) systems, there are multiple transmit antennas and multiple receive antennas and a plurality of sub-carriers that are available for transmission between the transmit antennas and the receive antennas for either one or multiple users. New advances in MIMO OFDM systems are taught in U.S. patent application Ser. No. 10/593,053 entitled “Pilot Design For OFDM Systems With Four Transmit Antennas” filed Mar. 15, 2005, and in PCT Patent Application No. PCT/CA2005/000507 entitled “Wireless Communication Methods, Systems, And signal Structures” filed Apr. 4, 2005, both hereby incorporated by reference in their entirety. With open loop implementations, the transmitter transmits on the multiple transmitter antennas and sub-carriers without the benefit of channel information fed back from the receivers.
Efforts have been made to facilitate wireless closed-loop MIMO communications including broadband closed-loop MIMO, which might for example be based on OFDM modulation schemes, and narrowband closed-loop MIMO. Broadband closed-loop MIMO includes many sub-bands. Each of these sub-bands requires MIMO channel feedback for a closed-loop implementation. As a result the feedback resources required for broadband closed-loop MIMO can become quite large. Narrowband closed-loop MIMO, by comparison, includes one or a few sub-bands and requires a relatively smaller amount of feedback resources. Broadband and narrowband MIMO, therefore, have different applications.